The term “physiologically active agent” used hereinafter includes any compound or composition of matter which, when administered to an organism (human or animal subject) induces a desired pharmacologic and/or physiologic effect by local and/or systemic action. The term therefore includes those compounds or chemicals traditionally regarded as drugs, biopharmaceuticals (including molecules such as peptides, proteins, nucleic acids), vaccines and gene therapies (e.g. gene constructs). When the agent is provided in powdered form, the size of the powder is affected by its delivery route. For pulmonary delivery the optimum particle size is 1-5 μm, whereas for nasal delivery the optimum size is believed to be 10-20 μm. A suitable amount for a single dosing event is of the order of 100's of μg to 10's of mg.
It has been recognised that nasal delivery provides an excellent route for delivering some physiologically active agents into the human system in addition to topical treatment. For example, advantages of nasal delivery include high permeability of the nasal cavity compared with the gastro-intestinal tract, the highly vascularised subepithelial layer in the nasal mucosa and high patient compliance compared with injection. This can lead to potentially greater therapeutic effect, the requirement for potentially smaller doses and rapid systemic absorption. There is a demand amongst pharmaceutical companies for nasal drug delivery devices which have some of the following properties: smaller delivery volumes, increased dosing accuracy, an avoidance for a need to prime device, prevention of bacteriological contamination and performance that is independent of the user.
Dry powders of physiologically active agents generally offer advantages over liquid formulations in nasal delivery, these advantages including longer retention in the nasal cavity, better absorption of some agents, use of higher concentrations of agent, minimisation of problems associated with liquid running back out of the nose and improved stability of the physiologically active agent when stored in dry form.